1. Field of the Invention
The present invention relates to an ocular light stimulus apparatus, and more particularly relates to an ocular light stimulus apparatus for irradiating an ocular fundus of an examinee's eye with fundus observation light and stimulus light through an objective lens, and locally stimulating a retina with the stimulus light to carry out a biological examination using a bioelectric signal from the retina.
2. Description of the Prior Art
In addition to fundus examinations by photographing an ocular fundus image, conventionally known opthalmological examinations primarily include an electroretinogram (ERG) examination in which the retina is irradiated with stimulus light to measure an action potential generated in the retina in order to carry out an opthalmological biological examination.
In an ERG examination, background light is required for illuminating the background irradiated with stimulus light, and the quality of the ERG examination is affected by the proper combination of intensity of the background light and intensity of the stimulus light. The Journal of Japanese Opthalmological Society, v92(9) (Sep. 10, 1988; from 5-(1423) to 11-(1429)) describes an effect in which visible light is used as the background light when an ERG examination is carried out by locally irradiating the macular spot on the ocular fundus with stimulus light (local ERG).
Japanese Examined Patent Publication No. 1987-16090 describes a configuration in which the ocular fundus of the examinee's eye is irradiated with stimulus light using a fundus camera, and electrical information obtained by light stimulus is displayed as an electroretinogram. Japanese Examined Patent Publication 1987-20809 proposes a configuration for observing the state and location stimulated by the local ERG stimulus light while observing a wide range of the ocular fundus using infrared light.
Furthermore, Japanese Examined Patent Publication No. 1992-19852 describes a configuration in which the ocular fundus of the examinee's eye is observed in a non-mydriatic state, and a beam of light for observing and photographing the examinee's eye is used as stimulus light. Japanese Unexamined Patent Publication No. 2005-323815 describes a configuration in which a light stimulus apparatus for irradiating the ocular fundus with stimulus light is mounted onto a fundus camera as a unit to carry out an ERG examination. Japanese Unexamined Patent Publication No. 2006-42952 discloses that the entire retinal region is irradiated with white light using a white light-emitting diode, and using this as background light, a spotlight from a high-brightness light-emitting diode is projected as stimulus light to perform a local ERG examination while observing the ocular fundus using infrared light.
A configuration is also known in which background light is projected onto the ocular fundus through an objective lens, a light source is provided at the periphery of the objective lens, and the background light is projected onto the ocular fundus from the light source (Journal of Japanese Opthalmological Society, v85(10) (Oct. 10, 1981; 9-(1521) to 19-(1531)).
As described in the Journal of Japanese Opthalmological Society, v85(10) (Oct. 10, 1981; 9-(1521) to 19-(1531), background light having a proper intensity is projected onto the ocular fundus prior to examination when an ERG examination is to be carried out. The background light is projected in advance so as to allow the examinee's eye to adapt to the light. However, since the background light is visible, there is a problem in that the internal fixation lamp is difficult to see when the background light is projected onto the ocular fundus during fundus observation. The examinee's eye does not stably fixate, and a biological examination is difficult to carry out with accurate alignment and reliability.